The goal of this proposal is to develop, analyze, and test an innovative technique for measuring volume blood flow ultrasonically. The quantification of volumetric flow is useful for a number of clinical applications including estimation of cardiac output, monitoring of cerebrovascular diseases, and evaluation of intrauterine growth restriction (IUGR) during pregnancy. Current techniques for measuring volumetric flow are either invasive (i.e. insertion of a Swan-Ganz catheter) or have limited accuracy (i.e. calculations based on Doppler measurements). The long term goal of this project is to defme a real-time, angle-independent volumetric flow measurement technique that can be implemented with current clinical scanner architecture. The proposed algorithm incorporates steered Doppler with the decorrelation of the raw ultrasound RF signals to compute the 3-D vector velocity profile of a vessel using a single transducer. Integration of the normal flow component over a cross-section of the vessel provides the total volume flow. This study will test implementation using modified pulsing sequences and digital correlators currently used in standard Doppler ultrasound machines. The algorithm will initially be verified on steady flow of blood-mimicking fluids in phantoms. A permutation test will be used to determine optimal parameter settings and ifitering schemes. Pulsatile waveforms and velocities in physiological ranges will be examined for accuracy and temporal resolution. Validation of the technique in vivo will be done by measuring flow in canine arteries and comparing with electromagnetic flow cuff results. Final evaluation of the technique will involve a pilot study quantifying flow in grafts of human subjects undergoing dialysis.